This invention relates to the separation of liquid and solid components of a slurry or pulpy material by pressing. In some instances, e.g., the production of paper, it is desired to squeeze the moisture from a slurry to obtain a solid product. In other instances, e.g., the production of fruit juice, it is desired to squeeze the pulp and collect the juice therefrom.
In either case, in order to be commercially practicable, the process must result in a rapid separation of the liquid and solid components of the product and must have an adequate degree of such separation.
Many products to be pressed are complex organic or inorganic materials, and the quality of the resulting liquid, or solid, is just as important as the quantity of the liquid, or solid, produced per unit time.
Wine grapes, from which the juice is to be squeezed and used in the making of wine, are a typical example of a product wherein the quality of the produced juice is very important.
Various continuous presses have been developed and used for extracting juice from grapes. For example, screw presses having a screw rotating in a perforated cylinder allow grape pulp to be fed continuously thereto, the pulp being compressed to a greater and greater degree to squeeze the juice therefrom as the pulp moves through the press. Such presses are capable of rapid and adequate separation of the juice from the seeds and skins of the grapes. However, the quality of the juice is impaired by the abrasive action of the screw in the perforated cylinder which releases tannin and other unpalatable substances from the skins and seeds.
"Basket" presses (referring to the wooden, cylindrical, spaced-stave presses of history) are generally used wherein the quality of juice is important. Such presses have a piston, or opposed pistons, reciprocating on the axis of a perforated or slotted cylinder to apply pressure to a batch of pulp and force the juice therefrom. In such operation the juice quality is high because there is very little abrasion of the solid components and the cake of compressed seeds and skins which is formed as squeezing progresses acts as a filter pad to retain minute solid particles of skins and pulps which would otherwise contaminate the extracted juice. However, such presses are inherently slow in operation since they are limited to operation on a single batch at a time. After each squeezing, the resulting cake must be removed, usually by hand, before a new batch may be pressed. Moreover, such presses are usually quite large in size so that a large quantity of pulp may be operated upon at one time. As a result, the large average distance that juice in the batch must travel in order to be discharged substantially increases the time required to obtain an adequate degree of separation of the juice from the pulp. Furthermore, with large-size presses, pockets of trapped fluid will develop in the batch, which reduces the efficiency of fluid removal.
In recent years efforts have been made to mechanize basket-type presses to reduce or eliminate the manual labor of digging the compressed cake resultant from each pressing, and to release trapped juice. Such presses usually involve opposed pistons reciprocating in a slotted or perforated cylinder. These presses are invariably large (typically a meter or more in diameter) to admit a large batch, and successively press and repress the pulp between the opposing cylinders. Chains and/or rods between the pistons fracture the cake each time the pistons withdraw. The cylinder then rotates to tumble and break up the cake before the next pressing stroke.
Such design does achieve a greater degree of separation and a higher rate of production per unit time, but two quality disadvantages are introduced thereby. The lengthy time per batch means prolonged exposure of the juice to oxidation. Further, the fracturing, tumbling and repetitive repressing of the restructured cake diminishes its capability as a filter pad, releasing minute solid particles which contaminate the extracted juice.
It is the principal object of the invention to provide an apparatus for separating liquid and solid components of a pulp which have the desirable attributes of a continuous press, i.e., a rapid and high degree of separation of the solid and liquid components while retaining the desirable quality attribute of a single-stage basket press wherein the resultant cake acts as a filter pad to prevent minute solid particles from contaminating the extracted juice.